One of the major problems in the electric power transmission industry is the damage caused by different types of wind-induced transmission line conductor motion. This wind-induced motion can lead to problems such as phase-to-phase faults, transmission line damage, and transmission line tower metal fatigue due to large, relatively rapid periodic motions of the conductors. The problem is widespread enough that power administration agencies all over the world have looked for ways to gather data on such transmission line conductor motion in an attempt to reduce or eliminate the motion and its associated problems.
One particularly severe type of wind-induced transmission line motion is a condition known as galloping. Essentially, galloping occurs when wind impinges upon an iced conductor line, often causing induction of lift in much the same manner as lift is induced on an airplane wing. The wind-induced lift caused during galloping causes the conductor to twist as it moves, and this twisting results in primarily vertical oscillation of the conductor. These oscillations can become quite complex, and often lead to the types of problems discussed above, including phase-to-phase faults and transmission tower damage. The need for a means of monitoring and controlling the conditions cause by galloping is of utmost importance in the power transmission industry.
Unfortunately for investigators in this area, the conditions under which galloping occurs are relatively rare. Among these conditions are the need for temperatures to be within a fairly narrow range centered around zero degrees centigrade, the presence of rain or sleet which allows for ice to form, and the wind impinging upon the power line must be coming from only particular directions. Because of these requirements, transmission line galloping seldom occurs when people are around to observe it. As a result, methods of detecting galloping and notifying potential observers or investigators have involved remote sensing and signalling of the conditions.
The most popular method used at present to detect galloping involves the installation of load cells on transmission towers associated with lines where galloping is suspected to occur. In this method, load cells are installed in the insulator string of the transmission tower, and the cell output triggers a signalling device such as a radio which alerts a remote observer to the condition. At this point, an observer or investigator can travel to the site where galloping is occurring in order to monitor and record the phenomena and its effects. The load-cell method, however, suffers from several drawbacks. In particular, the line which is to be monitored must be deenergized, or other safety precautions must be taken, when installation of the load cell occurs. Also, the signal cabling must be run from near the top of the tower to the signalling device, which increases the dangers involved in the cell installation. Furthermore, a bucket truck is required to be brought to the site, no matter what the topography of the particular area is. There clearly exists a need for developing a remote motion sensor for sensing the conditions associated with galloping which does not involve the potentially hazardous or inconvenient installation of sensors on transmission towers.
Other devices and systems are known in the patent art for monitoring power line conditions, but these U.S. Pat. No. 4,135,152 (Stuchly, et al.) and U.S. Pat. No. 4,087,701 (Anderson) both disclose power line monitoring devices which operate by means of a remote line-mounted sensor. Additionally, U.S. Pat. Nos. 4,158,810 (Leskover) and 3,197,702 (Schweitzer, Jr.) disclose telemetering posts for transmission lines which have line-mounted sensors. What is desired, therefore, is the development of a system which employs a ground-based sensor which can effectively monitor wind-induced line conductor motion conditions such as galloping, yet which avoids the problems and hazards associated with the previously used remote line- or tower-mounted sensing devices.